HONG KONG—Public anger at Hong Kong’s police force is increasingly driving a protest movement that began as peaceful opposition to Beijing’s growing influence over this city’s affairs.

That fury was on full display after police shot a 21-year-old protester at close range on Monday, marking the third such incident during this year’s unrest and triggering more clashes throughout the day. The man, identified by friends as Patrick Chow, a hotel-management student, remained in critical condition after undergoing an emergency surgery.

Trust in Hong Kong’s police force has plunged since police first used tear gas against protesters in June, polls show, and officers now routinely use rubber bullets, batons and water-cannon blasts while trying to disperse and arrest protesters. Police have become the most visible enemy for radical protesters, particularly black-clad youths flinging Molotov cocktails and bricks.

The police force has repeatedly said it uses the minimum force necessary to maintain order and has blamed the violence on protesters. Regarding Monday’s shooting, police said the officer fired because the protester was trying to grab his gun. Later in the day, they showed footage of a 57-year-old man who was set ablaze shortly after confronting protesters.

The tensions rose in recent days after a university student died of injuries sustained during a fall at a parking garage while officers nearby were dispersing protesters.

On Monday, hundreds of office workers lined up alongside more violent protesters in the city’s Central district to hurl abuse at police officers in riot gear. Participants in the protest movement are demanding a judge-led independent investigation into allegations of excessive force and brutality.

A Hong Kong police officer fired bullets at protesters early Monday, leaving one man in critical condition. The city’s regional commander said the officer was trying to keep his gun from being snatched. Hong Kong Chief Executive Carrie Lam on Monday evening said the government won’t give in to violence. Photo: Cupid Producer

Hong Kong’s leader, Chief Executive

Carrie Lam,

reiterated Monday that a probe by the existing Independent Police Complaints Council must run its course before any other investigations can be considered. The council is due to issue an initial report in the next few weeks.

Critics say the council lacks resources and powers such as summoning witnesses. Those concerns were shared in recent days by an international panel of experts called in by the government to advise the council on its investigation.

In a tweet on Saturday, Clifford Stott, one of the experts and a social-psychology professor researching public-order policing at Britain’s Keele University, shared a statement from the panel that called into question the council’s ability to conduct independent investigations into policing practices, given the scale of events in Hong Kong and the council’s restrictions on collecting and validating evidence.

With the government refusing to establish such an inquiry, public anger has risen as police have drawn weapons during skirmishes with demonstrators, shooting three protesters in recent weeks. A video clip of Monday’s shooting of the 21-year-old ricocheted around Hong Kong via cellphone. The sound of pistol fire could be heard on subway cars Monday morning as commuters watched footage of the scene.

Riot police securing a road in Hong Kong’s Central district of office buildings and luxury-retail stores on Monday.
Photo:

dale de la rey/Agence France-Presse/Getty Images

Anger was visible Monday in Tseung Kwan O, a dense community of apartment towers. A parking garage there has become a shrine for the university student who fell at the site and later died from his injuries. From mid-Monday morning, dozens of young protesters milled around outside the parking garage with bricks in their hands, expecting police to show up. Others gathered inside around the shrine of the student.

“We think the police just want to kill us all,” said an 18-year-old university student standing over the shrine. When police arrived outside, she pulled on a black sweatshirt and ran toward the developing front line.

Police fired tear gas in several directions, including into the garage. Protesters scattered into apartment towers. The tear gas wafted into residences, a primary school and secondary school, and a shopping arcade.

Local residents poured into the streets. Police attempted to enter the courtyards of apartments where protesters had fled, but were shouted back by the crowd. Outnumbered, the police retreated, sometimes leveling shotguns at the crowd.

Hong Kong’s police force was previously largely respected by citizens. But the force had limited exposure to dealing with violent disruptions until this summer and has been stretched thin from monthslong protests that take place several times a week.

Recent polls show that the police have lost the support of the majority of people in Hong Kong, with one October survey showing more than half of the 751 people interviewed have zero trust in the city’s police force, a sharp rise from 6.5% at the start of the summer.

Amnesty International called for an investigation into the police’s actions on Monday. “These are not policing measures—these are officers out of control with a mind-set of retaliation,” said Man-Kei Tam, director of Amnesty International Hong Kong.

The Hong Kong police spokesman dismissed the claim. “We are under great pressure. Our officers also encountered difficult times during the operations,” he said, adding that police have guidelines to use force as responsive measures.

Regina Ip, a pro-Beijing lawmaker and adviser to Mrs. Lam, said the priority of the Hong Kong police must be to quash unrest and restore order. “Police are not there to win a popularity contest. Their job is to enforce the law and maintain order,” she said.

Police officials have repeatedly pushed back against public criticism and blamed protesters for escalating violence. Earlier this month, the chairman of the Junior Police Officers’ Association, Lam Chi-wai, wrote an open letter to the group’s 25,000 members condemning what he called “crazed targeted attacks” and “smears” against the police. He praised fellow officers for “overcoming countless difficulties and performing duties professionally and in accordance with the law.”

A riot-police officer detaining a protester at a shopping mall in Tai Po in Hong Kong on Nov. 3.
Photo:

kim kyung hoon/Reuters

Those views were hard to come across at lunchtime on Monday in the Central district, an area crammed with offices and luxury retail stores. Outrage subsumed hunger for some office workers who streamed onto the streets to denounce what they called police violence.

Nearby stores shut down early, while traffic ground to a halt as protesters built barricades to block key roads. Police fired tear gas down one street, sending protesters and passersby scurrying to escape the choking fumes.

A 38-year-old entrepreneur, who gave his surname as Cheung, said he joined the protest after seeing television reports about the shooting while working at his office in Central. “The police are abusing their power,” he said. “This shouldn’t be happening in a civilized city.”